This invention relates to electronics, and more particularly to compositions useful for producing conductor patterns adherent to substrates.
Conductor compositions which are applied to and fired on dielectric substrates (glass, glass-ceramic, and ceramic) usually comprise finely divided inorganic powders (e.g., metal particles and binder particles) and are commonly applied to substrates using so-called "thick film" techniques, as a dispersion of these inorganic powders in an inert liquid medium or vehicle. Upon firing or sintering of the film, the metallic component of the composition provides the functional (conductive) utility, while the inorganic binder (e.g., glass, crystalline oxides such as Bi.sub.2 O.sub.3, etc.) bonds the metal particles to one another and to the substrate. Thick film techniques are contrasted with thin film techniques which involve deposition of particles by evaporation or sputtering. Thick film techniques are discussed in "Handbook of Materials and Processes for Electronics", C. A. Harper, Editor, McGraw-Hill, N.Y., 1970, Chapter 12.
The most commonly used conductor compositions employ noble metals, especially gold, silver, platinum, palladium, and their mixtures and alloys, since their relatively inert characteristics permit firing in air. Attempts at using dispersions of less expensive non-noble metals have often been confined to specialized uses or have required the great practical inconvenience and expense of firing in non-oxidizing atmospheres (nitrogen, nitrogen/hydrogen, hydrogen, argon, etc.).
The prior art on conductor compositions includes the use of glass binders for noble metals, as well as the use of glass-free binders. Martin U.S. Pat. No. 3,293,501 discloses conductive films of glasses comprising copper and bismuth oxides. Buck U.S. Pat. No. 3,776,769 discloses compositions of noble metal, copper oxide and glass, fireable in reducing atmospheres. Short U.S. Pat. No. 2,819,170 discloses compositions of silver and a vitrifiable flux of bismuth oxide and cadmium borate.
Conductor compositions are used in the microcircuit industry to "terminate" resistor patterns, typically by firing the conductor pattern on a substrate and then printing resistor patterns over part of the conductor pattern and firing. When typical Pd/Ag conductor compositions have been used as terminations for certain ruthenium based resistors (such as low-ohm, less than 100 ohms/square/mil of thickness, resistors of pyrochlore-related oxides or RuO.sub.2), staining of the surface of the conductive termination adjacent to the resistor often occurs during resistor firing.
Such surface stains are undesirable since they prevent complete soldering of the conductor in the region of the resistor. Bi.sub.2 O.sub.3 is present in typical conductor compositions to enhance adhesion, but it seems to be responsible for such staining. Elimination of Bi.sub.2 O.sub.3 from the compositions results in degradation of solder acceptance and adhesion of the conductor patterns to an unacceptable degree. The industry needs a Bi.sub.2 O.sub.3 -free termination material with good adhesion and soldering characteristics.